Enhanced-impact LLDPE with a shear modifiable network structure

ABSTRACT

The present invention provides an ethylene copolymer resin that has unique melt elastic properties not observed in ethylene copolymers heretofore known. Specifically, the ethylene copolymer resin of the present invention when in pelletized form has a reduction in melt elasticity (ER) of 10% or more to a final value of 1.0 or less upon rheometric low shear modification or solution dissolution. Moreover, the resin of the present invention when in reactor-made form exhibits at least a partially reversible increase of 10% or more in ER when pelletizing the same. An ethylene polymerization catalyst, a process of preparing the ethylene copolymer resin and a high-impact film are also provided herein.

This application is a division of application Ser. No. 09/205,481, filedDec. 4, 1998 now U.S. Pat. No. 6,171,993.

FIELD OF THE INVENTION

The present invention relates to an ethylene copolymer, and moreparticularly to an in-situ prepared ethylene copolymer resin which hasunique melt elastic properties when the resin is in its reactor-made orpelletized forms. The melt elastic properties observed by the ethylenecopolymer resin of the present invention are not found in ethylenecopolymers known heretofore, and importantly provide enhanced-impactstrength properties to films that are produced therefrom.

The present invention is also directed to a polymerization catalyst.

BACKGROUND OF THE INVENTION

The successful development of linear low density polyethylene (LLDPE)has forever changed the character of the polyethylene industry. For overfifty years, low density polyethylene (LDPE) was produced at pressuresranging up to 345 MPa (50,000 psi) and temperatures of about 300° C.Technology was then developed in subsequent years which was capable ofoperating at less than 2 MPa (300 psi) and near about 100° C., Thistechnologic development has rapidly established itself as a low costroute to producing LLDPE.

LLDPE, which is typically made using a transition metal catalyst ratherthan a free-radical catalyst, as required for LDPE, is characterized bylinear molecules having no long-chain branching; short-chain branchingis instead present and is the primary determinant of resin density. Thedensity of commercially available LLDPE typically ranges from0.915-0.940 g/cm³. Moreover, commercially available LLDPEs. generallyexhibit a crystallinity of from about 25-60 vol. %, and a melt indexwhich can range from 0.01 g/10 min. to several hundred g/10 min.

Many commercial LLDPEs are available which contain one or morecomonomers such as propylene, 1-butene, 4-methyl-1-pentene, 1-hexene,1-octene and mixtures thereof. The specific selection of a comonomer forLLDPE is based primarily on process compatibility, cost and productdesign.

In today's polyethylene industry, LLDPEs are used in a wide variety ofapplications including film forming, injection molding, rotomolding, andwire and cable fabrication. A principal area for LLDPE copolymers is infilm forming applications since such copolymers typically exhibit highdart impact, high Elmendorf tear, high tensile strength and highelongation, in both the machine direction (MD) and the transversedirection (TD), compared with counterpart LDPE resins.

Examples of previous developmental trends in this field include U.S.Pat. Nos. 5,26.0,245; 5,336,652; and 5,561,091, all to Mink et al.,which disclose LLDPE films that exhibit the above properties made frompolymerizing ethylene and at least one comonomer in the presence of a apolymerization cocatalyst and vastly distinct transition metalcatalysts. Specifically, in the '245 patent the transition metalcatalyst is formed by treating silica having reactive OH groups with adialkylmagnesium compound it a solvent; adding to said solvent acarbonyl-containing compound and then treating with a transition metalcompound.

In the '652 patent, the transition metal catalyst is prepared bytreating a support having a reduced surface OH content with anorganomagnesium compound; treating the product with a silane compoundhaving the formula R_(x) ¹SiR_(y) ² wherein R¹ is R_(w) ^(—)O whereR_(w) is hydrocarbyl containing 1 to 10 carbon atoms; R² is halogen,hydrocarbyl having 1 to 10 carbon atoms or hydrogen; x is 1, 2, 3 or 4and y is 0, 1, 2 or 3 with the proviso that x+y=4, and a transitionmetal compound. In this reference, reduction of surface OH content ofthe silica is effectuated by heating or by treatment with an aluminumcompound.

The transition metal catalyst employed in the '091 patent is one that isobtained by contacting silica having reactive OH groups with adialkylmagnesium compound in a solvent; adding a mixture of an alcoholand SiCl₄ thereto with subsequent treatment with a transition metalcatalyst.

U.S. Pat. No. 4,335,016 to Dombro provides a supported olefinpolymerization catalyst which is prepared by (1) forming a mixture of acalcined, finely divided porous support material and an alkyl magnesiumcompound; (2) heating the mixture for a time and at a temperaturesufficient to react the support and the alkyl magnesium compound, (3)reacting, by heating, the product of (2) with ahydrocarbylhydrocarbyloxysilane compound; (4) reacting, by heating, theproduct of (3) with a titanium compound that contains a halide; or (5)reacting the product of (2) with the reaction product of ahydrocarbylhydrocarbyloxysilane compound and a titanium compound thatcontains a halide; and (6) activating the catalyst product of (4) or (5)with a cocatalyst comprising hydrogen or an alkyl lithium, alkylmagnesium, alkyl aluminum, alkyl aluminum halide or alkyl zinc.

Crotty et al. “Properties of Superior Strength Hexene Film Resins”,Antec, 193, pp. 1210 describes the properties of superior strengthhexene copolymer resins that are prepared by the Unipol process. Theseresins reportedly yield films with exceptional strength properties(impact and tear strength) that are significantly higher than thestandard hexene products and even higher than achieved with commerciallyavailable octene copolymers. At the same time, the resins show little orno difference in processability from standard LLDPE.

The actual physical structures of polymers and abundant changes to sameunder various conditions is difficult to measure precisely and iscommonly done indirectly. Rheology is often used in this regard, beingespecially suited to study the physical changes of polymers.Specifically, rheology deals with the deformation and flow of a polymer.Data so generated is used to provide information regarding theprocessability and even structural characterizations of the polymer.

One Theological method that is typically used is conventional, highshear modification wherein disentanglement of the polymer or copolymerchains occur. If a polymer or copolymer melt is sheared mechanically,the melt may be processed in a less elastic state or possibly lessviscous state than the initial resin. Effects of shear modification aretypically manifested by changes in die swell, die entrance pressurelosses, normal stresses and flow defects such as sharkskin surfaces andmelt fracture.

Although shear modification has been observed in LDPE, whereindisentanglement of the long chain branching of the polymer can readilyoccur, there was contention as to whether LLDPE could be shear modified.The question was answered in an article by Teh, et al. entitled “ShearModification of Linear Low Density Polyethylene”, Plastics and RubberProcessing and Applications, Vol. 4, No. 2, pg. 157 (1984). In thisarticle, LLDPE was shear modified by preshearing the LLDPE resin underhigh shear conditions (>3.9 sec⁻¹) in an extruder. This study indicatedthat shear modification of the LLDPE polymer causes disentanglement tooccur in the extruder, and that the relatively, disentangled polymer canbe restored to a more highly elastic, entangled state by subjecting themelt to annealing or dissolving the shear modified polymer in a solvent.

Another rheological technique employed in the prior art to determine thephysical characteristics of a polymer is to measure the polydispersityor melt elasticity, ER, of the polymer melt. This technique is describedin an article by R. Shroff, et al. entitled “New Measures ofPolydispersity from Rheological Data on Polymer Melts”, J. AppliedPolymer Science, Vol. 57, pp. 1605-1626 (1995).

Using this Theological technique (ER calculation), prior art ethylenecopolymer resins, such as described in Teh, et al., exhibit conventionalmelt elastic behavior in both the unsheared pelletized and shearedpelletized states. In the unsheared state, the ER values of prior artethylene copolymers remain substantially unchanged in going from thepowder to pellet form. Moreover, no change in ER is observed indissolving the pellet in an organic solvent.

As to the shear modified forms, prior art polymers exhibit a decrease inmelt elasticity upon shear modification of the pelletized form. Thissignifies that the entanglement density of the polymer decreases. Upondissolution of the shear modified form in an organic solvent, anincrease in melt elasticity is observed with prior art ethylenecopolymers. This increase in melt elasticity signifies a reversion ofthe polymer back to an entangled state.

In prior art ethylene copolymers, no polymeric networks, i.e. systems ofinterconnected macromolecular chains, are present. This is verified bythe above melt elastic behavior of prior art ethlylene copolymers. As isknown to those skilled in the art, the presence of network structures inpolymers often provides polymers having improved properties. It isemphasized that while network structures are common instyrene-butadiene-styrene (SBS) block copolymers—See F. Morrison, etal., “Flow-Induced Structure and Rheology of a Triblock Copolymer”, J.Appl. Polymer Sci., Vol. 33, 1585-1600 (1987)—they are not known inLLDPE resins, until the advent of the present invention.

SUMMARY OF THE INVENTION

The present invention provides an ethylene copolymer that exhibitsunique melt elastic properties that are not present in ethylenecopolymers known heretofore. The unique melt elastic properties that areexhibited by the inventive ethylene copolymer are believed to bemanifested by the presence of a network structure in the copolymerresin. While not being bound by any theory, it is hypothesized that thenetwork structure in the present ethylene copolymer is formed at leastin part of a rubber phase believed present in the copolymer which servesto interconnect the hard and soft phases of the ethylene copolymer.

The presence of a network structure in the ethylene copolymer resin ofthe present invention is verified by the fact that the copolymer resinexhibits a reactor-made-to-pellet ER increase which is reversible, i.e.reduced, upon rheometric low shear modification. The term “ER” is usedherein to measure the elasticity or the polydispersity of the ethylenecopolymer which is derived from rheological data on polymer melts, Seethe article to Shroff, et al. supra. The term “reactor-made” is usedherein to denote powder, slurry or solution forms of the polymer resinwhich are formed in a polymerization vessel prior to melt processing.

In addition to exhibiting, the above melt elastic behavior, thepelletized form of the ethylene copolymer of the present inventionexhibits a decrease in melt elasticity when dissolved in an organicsolvent such as xylene. The solution dissolution ER value is nearly thesame as that of the original reactor-made material.

Specifically, the ethylene copolymer resin of the present inventioncomprises ethylene, as the major component, and at least one C₄₋₈comonomer with the proviso that the resin, when in pelletized form, hasa reduction in melt elasticity (ER) of 10% or more, to a final ER valueof 1.0 or less upon rheometric low shear modification or solutiondissolution. A 10-30% reduction in ER of the pelletized form of theinventive copolymer resin upon rheometric low shear modification orsolution dissolution is typically observed. Moreover, the ethylenecopolymer resin of the present invention, when in reactor-made form,exhibits a partially reversible increase of 10% or more in said ER whenpelletizing the same.

The term “rheometric low shear modification” is used in the presentinvention to indicate that the modification occurs in a rheometer thatis capable of operating at shear rates of less than 1.0 sect for a timeperiod of from about 10 to about 60 minutes. This term is thusdistinguishable from high shear modification, as disclosed in Teh, etal., supra, wherein the modification is typically carried out in anextruder, prior to being introduced into a rheometer, at shear rates of3.9 sec⁻¹ and higher.

The term “solution dissolution” is used herein to indicate that thepelletized form of the ethylene copolymer resin can be dissolved in anorganic solvent such as xylene. The importance of this technique is thatit allows a means for estimating the ER value of the originalreactor-made material if the same is not available.

In addition to exhibiting unique melt elastic properties, the ethylenecopolymer resin of the present invention is further characterized ashaving a base polymer density of about 0.930 g/cm³ or less, a melt indexof from about 0.01 g/10 min or greater and a rubber content of about 15vol. % or greater. Moreover, the rubber phase of the ethylene copolymerresin of the present invention contains from about 35 to about 65 alkylbranches per 1000 total carbon atoms.

Another aspect of the present invention relates to a high-impactstrength film that can be produced from the ethylene copolymer resin ofthe present invention. The term “high-impact strength” is used herein todenote an impact strength, as measured using a free-falling dart, of atleast about 30.0 g/mil or higher.

Another aspect of the present invention relates to a polymerizationcatalyst which, among other things, is capable of producing ethylenecopolymers having the unique melt elastic properties mentioned above. Inone embodiment of the present invention, the ethylene polymerizationcatalyst is obtained by:

(a) contacting a support material with an organosilicon compound toeffectuate reduction of surface hydroxyl groups present on said supportmaterial;

(b) contacting the modified support material with a dialkylmagnesiumcompound or complex;

(c) contacting the product of (b) with an alcohol or ahydrocarbyloxyhydrocarbylsilane; and

(d) contacting the product of (c) with a transition metal compound.

In another embodiment of the present invention, the polymerizationcatalyst is obtained by:

(a) contacting a support material with an organosilicon compound toeffectuate reduction of surface hydroxyl groups present on said supportmaterial;

(b) contacting the modified support material with a dialkylmagnesiumcompound or complex;

(c) contacting the product of (b) with a transition metal compound; and

(d) contacting the product of (c) with an alcohol or ahydrocarbyloxyhydrocarbylsilane.

In yet another embodiment, the catalyst of the present invention isobtained by:

(a) contacting a support material with an organosilicon compound toeffectuate reduction of surface hydroxyl groups present on said supportmaterial;

(b) contacting the modified support material with an alcohol or ahydrocarbyloxyhydrocarbylsilane;

(c) contacting the product of (b) with a dialkylmagnesium compound orcomplex; and

(d) contacting the product of (c) with a transition metal compound.

It is emphasized that in the embodiments wherein an alcohol is employedin preparing the polymerization catalyst, a hydrocarbyl alkoxysilanecocatalyst modifier such as diisopropyldimethoxysilane (DIPS) isrequired to be used.

A still further aspect of the present invention relates to an ethylenepolymerization process wherein ethylene and at least one C₄₋₈ comonomerare copolymerized in the presence of one of the above-mentioned ethylenepolymerization catalysts, a suitable cocatalyst capable of activatingthe ethylene polymerization catalyst and, optionally, a cocatalystmodifier. This polymerization process results in the production of theinventive ethylene copolymer resin having the unique melt elasticproperties described hereinabove.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of film impact (g/mil) vs. resin density (g/cc) forvarious catalyst systems.

FIG. 2 is a graph of film impact (g/mil) vs. vol. % rubber for variouscatalyst systems.

FIG. 3 is a graph of vol. % rubber vs. resin density (g/cc) for variouscatalyst systems.

FIG. 4 is a graph of film impact (g/mil) vs. rubber interparticledistance (micrometers).

FIG. 5 is a graph of %ER shift(powder-to-pellet) vs. powder ER forvarious catalyst systems.

FIG. 6 is a graph of pellet %ER reduction upon shear modification vs.pellet ER after rheometric shear modification for various catalystsystems.

DETAILED DESCRIPTION OF THE INVENTION

As stated above, the present invention provides an ethylene copolymerresin which exhibits enhanced film impact when formed into a film, andhas unique melt elastic properties which, in part, signify the presenceof a network structure in the ethylene copolymer resin of the presentinvention.

The ethylene copolymer resin of the present invention is characterizedas containing ethylene, as the major component, and at least one C₄₋₈comonomer, as a minor component. In accordance with an embodiment of thepresent invention, it is highly preferred that 1-hexene be used as thecomonomer. When 1-hexene is employed as the comonomer, the resintypically contains 95% or less ethylene and the remainder being1-hexene.

Another characteristic of the ethylene copolymer resin of the presentinvention is that it has a base copolymer density of about 0.930 g/cm³or below. The term “base polymer density” represents the density of thepolymer resin before the addition of any additives or fillers which arecommonly introduced upon processing. More preferably, the base polymerdensity of the ethylene copolymer resin of the present invention isabout 0.920 g/cm³ or below. Most preferably, the base polymer density isabout 0.917 g/cm³ or below. The above density ranges qualify theethylene copolymer resin of the present invention as LLDPE.

In addition to the above characteristics, the ethylene copolymer resinof the present invention also contains a network structure which isbelieved, but not entirely known, to be formed at least in part by arubber phase known to be present in the inventive ethylene copolymerresin. The rubber phase is characterized as being an ethylene/comonomerrubber which is highly branched, i.e. it contains from about 35 to about65 alkyl branches per 1000 total carbon atoms. The network structure isbelieved to interconnect the hard and soft phases of the inventivecopolymer resin thereby partly providing the ethylene copolymer resin ofthe present invention with its unusual and totally unexpected meltelastic properties.

In one embodiment of the present invention, the ethylene copolymer resincontains about 15 vol. % or greater of a rubber phase, as measured by atechnique known as Scanning Electron Microscopy (SEM) which isdescribed, for example, in an article to F. Mirabella, et al. entitled“Morphological Explanation of the Extraordinary Fracture Toughness ofLinear Low Density Polyethylenes”, J. Polymer Science: Part B: PolymerPhysics, Vol. 26, No. 9, August 1988, pp. 1995-2005. Specifically, thefollowing procedure was employed in the present invention to determinethe vol. % rubber in the copolymer resin: A compression-molded samplewas microtomed at a specimen temperature of about −80° C. in an LKBUltratome V with Cryokit. The bulk specimen thus prepared was etched inn-heptane at 60° C. for 20 minutes in a sonic bath, mounted onto ascanning electron microscope specimen stub, and sputter coated withapproximately 200 Å of gold. The specimen was then analyzed in an ISI-40SEM. This procedure removes any rubbery, amorphous or low-crystallinity,in the resin from the specimen surface and leaves definable cavitieswhere the material was originally located. Photomicrographs werestatistically analyzed with a Ziess Videoplan Image Analyzer.

In one embodiment of the present invention, the rubber particles presentin the ethylene copolymer resin of the present invention have an averageradius, R_(w), of about 0.05 to about 0.25 micrometers. Theinterparticle distance of the rubber particles in the rubber phase isdetermined using the following equation:${{Interparticle}\quad {distance}} = {2R_{W}\left\lfloor {\left( \frac{\pi}{6\varphi} \right)^{1/3} - 1} \right\rfloor}$

where R_(w) is the average particle radius and φ is the volume fraction(vol. % rubber/100), See S. Wu “Phase Structure and Adhesion in PolymerBlends: A Criterion for Rubber Toughening”, Polymer, Vol. 26, pp. 1855(1985). In one embodiment of the present invention, the rubber particlestypically have an interparticle distance of 0.20 micrometers or less.

The ethylene copolymer resin of the present invention is furthercharacterized as having a melt index of from about 0.01 g/10 min. orgreater. More preferably, the ethylene copolymer resin of the presentinvention has a melt index of from about 0.5 to about 4.0 g/10 min.

Although various of the above resin properties may be known in the art,the unique melt elastic properties defined hereinbelow are not. It isthis characteristic of the inventive ethylene copolymer resin whichdistinguishes same from all previously known ethylene copolymers.

Specifically, the ethylene copolymer resin of the present invention,when in reactor-made form, has a ER value of 0.9 or below, whichundergoes an increase in ER when pelletizing the reactor-made material.That is, when the original reactor-made form, i.e. powder, solution orslurry, of the ethylene copolymer resin of the present invention is madeinto a pellet one observes a positive %ER shift. An increase from about10 to about 80% in ER is typically observed when comparing thereactor-made material to the pellet. However, such an increase isreversible. That is, the pellet's ER value can be reduced uponrheometric low shear modification or solution dissolution. Thischaracteristic is distinct from irreversible increase in ER observed,for example, due to polymer degradation (chain extension and/or longchain branching formation).

In addition to the above melt elastic property, the ethylene copolymerresin of the present invention, when in pelletized form, exhibits areduction in ER to values below 1.0 after subjecting the same torheometric low shear modification or solution dissolution. A 10-30%reduction in ER of the pelletized form of the invention copolymer resinis typically observed. This reduction in ER of the pelletized sampleunder rheometric low shear modification or solution dissolutionsignifies that the ER shift observed is reversible.

The following techniques were employed in the present invention toobtain rheological data of the ethylene copolymer resin of the presentinvention.

I. Xylene Dissolution Experiments: 2 grams of polymer were dissolvedinto 200 ml of xylene at 110° C. for about 1 hr. The resultant solutionwas allowed to cool at room temperature. The xylene solvent was allowedto slowly evaporate (typically over a period of 4-5 days). The polymersample was recovered and dried in vacuum at 60° C. for about 72 hours.The dried sample was then pressed into 25 mm disks for rheologicalmeasurements as described hereinbelow.

II. Sample Preparation for Rheological Measurements: Measurement ofpolymer melt rheological properties were carried out in a RheometricARES rheometer using 25 mm disk samples having a thickness of about 1.2mm. The disk samples were prepared by pre-pressing (pellet or powder, asnecessary) using a compression press and a brass 1.2 mm template with 1inch holes sandwiched between two ¼ inch steel plates with a sheet ofmylar film placed between the press template and; steel plates. About2-3 wt. % antioxidant (50% BHT-50% Irganox 1010) was added during diskpressing for extra stabilization. The compression press was maintainedat 150° C.

For polymers exhibiting powder-to-pellet changes in rheology, it isimperative to minimize flow and mixing during sample preparation. Forexample, pressing disks out of a polymer powder and then re-melting andrepressing the same disks may increase the measured ER.

III. Rheological Measurements for ER Calculation: A standard practicefor measuring dynamic rheology data in the frequency sweep mode, asdescribed in ASTM 4440-95a, was employed herein. A Rheometrics ARESrheometer was used, operating at 150° C., in the parallel plate mode ina nitrogen environment (in order to minimize sampleoxidation/degradation). The gap in the parallel plate geometry wastypically 1.2-1.4 mm and the strain amplitude was 10-20%, preferably 10%strain amplitude was employed. The range of frequencies was 0.0251 to398.1 rad/sec.

As disclosed in Shroff, et al. supra and U.S. Pat. No. 5,534,472 (SeeCol. 10, lines 20-30), ER is calculated from the storage modulus (G′)andloss modulus (G″) data, as follows: the nine lowest frequency points areused (5 points per frequency decade) and a linear equation is fitted byleast-squares regression to log G′ versus log G″. ER is then calculatedfrom the following equation:

ER=(1.781×10⁻³)×G′, at a value of G″=5000 dyn/cm².

It is understandable to those skilled in the art that nonlinearity inthe log G′ versus log G″ plot will result in different ER valuesdepending on the range of the data employed, which in turns relates tothe range in frequency data. The procedure followed was to extend thelower end of the frequency range so that the lowermost G″ value waswithin the range of 7-10³-10⁴ dyn/cm². Practically speaking, thisrequires a lowermost frequency of 0.0398 rad/sec for 1 MI LLDPEs and0.0251 rad/sec for 0.6 MI LLDPEs, at 150° C.

IV. Rheometric Shear Modification: A sample was placed in the AERSrheometer and a standard frequency sweep was performed. Then, a steadypreshearing was applied by specifying the shear rate and time ofpre-shearing. Typically, the shear rate was 0.1 sec⁻¹ and the time was20-60 minutes. Preshearing was applied by specifying the rotationalspeed of the moving plate in the Rheometrics ARES rheometer. Arotational speed of about 0.01 rad/sec will result in a shear rate of0.1 sec⁻¹ for a 1.25 mm gap and 25 mm plates. At the end of preshearing,a standard frequency sweep was performed. Comparison of the rheometricdata before and after rheometric shear modification and calculationcomparison of ER calculated from each, will show and quantify whetherthe polymer exhibits rheometric shear modifiability.

The above provides a description of the ethylene copolymer resin of thepresent invention, the description that follows, is directed to thepolymerization catalyst, polymerization process and film. The ethylenecopolymer resin of the present invention is prepared in-situ bypolymerizing ethylene and at least one C₄-C₈ comonomer in the presenceof an ethylene polymerization catalyst, a cocatalyst, and an optionalcocatalyst modifier, under ethylene polymerization conditions.Mechanical blends of ethylene and various comonomers and/or copolymerssuch as ethylene propylene rubber (EPR) fall outside the realm of thepresent invention since they are not prepared in-situ.

In one embodiment, the ethylene polymerization catalyst of the presentinvention is preferably prepared by contacting a chemically treatedsupport material with a dialkylmagnesium compound or complex, contactingthe magnesium-containing support material with either an alcohol or ahydrocarbyloxyhydrocarbylsilane and thereafter with a transition metalcompound. It is again emphasized that when an alcohol is used, ahydrocarbyl alkoxysilane cocatalyst modifier is required.

Suitable support materials that may be employed in the present inventioninclude: inorganic supports such as silica, alumina, aluminum phosphate,celite, magnesium oxide, iron oxide and organic supports includingpolymers and copolymers.

A preferred support material is silica. When silica is employed as thesupport material, it preferably pure, however, the silica may containminor amounts of other inorganic oxides. In general, the silica supportcomprises at least 90-95% by weight pure silica. In a preferredembodiment, the silica is at least 99% pure.

The silica support utilized in the present invention has a surface areaof from about 50 to about 500 m²/g; a particle size of from about 10 toabout 200 micrometers; and a pore volume of about 0.5 to about 3.0 cc/gas determined by standard B.E.T. measurements.

Another particularly preferred support material is celite. Celite is adiatomaceous earth composition composed of approximately 4% alumina,approximately 90% silica and the remainder calcium oxide and otherinorganic oxides. Celite, commercially available from Eagle-PicherMinerals, Inc., has a porosity of between about 50 to about 90 volume %;a pore volume of between about 2.4 to about 3.5 cc/g; and a surface areaof between about 2 to about 100 m²/g.

The aluminum phosphate, when employed as the support, has a preferredpore volume of between about 0.7 to about 1.25 cc/g and a preferredsurface area of about 200 to about 350 m²/g. To obtain these preferredphysical characteristics, it is preferred that the aluminum phosphate bemade more amorphous than pure aluminum phosphate. Thus, AlPO₄ issynthesized with other agents such that the atomic ratio of phosphorusto aluminum be in the range of between about 0.70 and about 0.95. Morepreferably, this atomic ratio is in the range of between about 0.72 andabout 0.85.

The alumina employed for use as the support is characterized by a porevolume of between about 0.8 to about 3 cc/g and a surface area of about300 m²/g to about 400 m²/g.

Prior to contact with the organomagnesium compound or complex, thesupport material is contacted with an organosilicon compound, such asdisclosed in U.S. Pat. Nos. 4,374,753 and 4,530,913 both to Pullukat, etal., the contents of each being incorporated herein by reference, toreduce the number of surface hydroxyl groups. Typically, about 0.3 toabout 1.2 mmol of OH groups remain after this chemical treatment step.It is noted that calcination alone or chemical treatment of a supportmaterial with an aluminum compound does not provide a polymerizationcatalyst which exhibits high activity and yield yet is capable ofproviding ethylene copolymers having all of the above mentionedcharacteristics.

Suitable organosilicon compounds that can be employed in the presentinvention to treat the support material are those having one of thefollowing formulas: (R₃ ⁴Si)₂NH, R₃ ⁴Si(OR⁴), R₃ ⁴SiX⁴ and (R₃ ⁴Si)₂Owherein R⁴ is alkyl or aryl, preferably each containing 1 to 20 carbonatoms, and X⁴ is a halogen. Specific examples of such organosiliconcompounds are hexaalkyl disilazane, trialkylsilyl ethoxide and alkylchlorosilanes of these, hexaalkyl disilazanes are particularly useful inthis application, with hexamethyl disilazane, i.e. HMDS, being highlypreferred.

After chemically treating the support material with an organosiliconcompound, the chemically modified support is optionally dried bycalcining the same in an inert atmosphere at a temperature of at least50° C. More, specifically, the calcining step is carried out at atemperature of from about 150° to about 650° C. in nitrogen or argon.The chemically treated support may optionally be dried by vacuum.

The chemically treated support material is then slurried in ahydrocarbon solvent, e.g. heptane or hexane, and thereafter treated witha dialkylmagnesium compound or complex having one of the followingformulas:

 R₂Mg; or

(R₂ ¹Mg)·nAlR₃ ¹

wherein R and R¹ are the same or different and each is independently analkyl containing from 1 to 12 carbon atoms and n is from 0.5 to 10. Ofthe compounds that satisfy the above formula, dibutylmagnesium sold byFMC Corporation, butylethylmagnesium and a complex of dibutylmagnesiumand triethylaluminum sold by Akzo Chemicals under the tradename MAGALAare highly preferred.

The amount of organomagnesium compound or complex added to thechemically treated support material is from about 0.01 to about 10 mmoleper gram support material. More preferably, the amount oforganomagnesium compound or complex added in making the ethylenepolymerization catalyst of the present invention is from about 0.5 toabout 1 mmole per gram support material.

The contact between the organomagnesium compound or complex and treatedsupport material usually occurs at a temperature range of between about15° to about 120° C. for a time period of from about 5 to about 180minutes. Preferably, this contact occurs at a temperature of from about20° to about 40° C. for a time period of from about 30 to about 60minutes.

To this contact product is added either an alcohol or ahydrocarbyloxyhydrocarbylsilane. When an alcohol is employed, aliphaticor aromatic alcohols containing from 1 to 12 carbon atoms can beemployed. For a complete description of this embodiment of the presentinvention, applicants refer to U.S. Pat. No. 4,374,753 to Pullukat, etal. which was previously incorporated herein by reference. In apreferred embodiment of the present invention, the alcohol is analiphatic alcohol containing 1 to 5 carbon atoms. Of these preferredalcohols, n-butanol, i.e. butyl alcohol, is most preferred. The amountof alcohol added to the organomagnesium-containing support reactionmixture is from about 0.1 to about 10 mmole per gram support material.More preferably, the concentration range of added alcohol is from about0.4 to about 1.0 mmole per gram support material.

The hydrocarbyloxyhydrocarbylsilane that can be employed in the presentinvention has the following formula:

(R²O)_(n)Si(R³)_(4-n)

wherein R² and R³ may be the same or different and are C₁-C₂₀ alkyl,cycloalkyl, aryl, alkaryl or aralkyl radicals, and n is from 1 to 4.Suitable compounds include: ethoxytrimethylsilane,diethoxydimethylsilane, triethoxymethylsilane, tetraethoxysilane (TEOS),diisopropyldimethoxysilane (DIPS), tetrabutoxysilane (TBOS),methoxytriphenylsilane, methyltriethoxysilane (MTEOS) andphenoxytrimethylsilane. Of these compounds, it is preferred to employTEOS or TBOS as the hydrocarbyloxyhydrocarbylsilane.

The silane compound is added in an amount of from about 0.05 to about 10mmole per gram support, with from about 0.1 to about 1 mmole per gramsupport being highly preferred.

The contact step between the organomagnesium-containing support contactreaction mixture and the alcohol or hydrocarbyloxyhydrocarbylsilaneusually occurs at a temperature range of from about 15° to about 120° C.for a time period of from about 5 to about 180 minutes. More preferably,this contact occurs at a temperature of from about 20° to about 40° C.for a time period of from about 30 to about 6.0 minutes.

The above contact product is then contacted with at least one transitionmetal compound belonging to Groups IVB and/or VB of the Periodic Tableof Elements. The transition metal compounds belonging to Group IVB ofthe Periodic Table of Elements have the structure formulaM′X_(p)(OR′)_(q) wherein M′ is titanium or zirconium; R′ is aryl, alkyl,aralkyl, cycloalkyl or alkylsilyl; X is a halogen; p is 0 or an integerfrom 1 to 4; and q is 0 or an integer from 1 to 4; with the proviso thatthe sum of p and q is 4. It is especially preferred that M′ be titanium.

In a preferred embodiment, the titanium-containing compound is onewherein p is an integer from 2 to 4 and q is 0 or an integer 1 or 2.Suitable titanium compounds within the contemplation of this embodimentare titanium tetrachloride, titaniumtetrabromide, methoxytitaniumtrichloride, ethoxytitanium trichloride, diethoxytitanium dichloride andthe like.

Still, more preferably, the titanium-containing compound is defined by pbeing 4, q being 0, and X is chlorine or bromine. Thus, the titaniumcompound is most preferably titanium tetrachloride or titaniumtetrabromide. Of these two titanium compounds, titanium tetrachloride ismost preferred.

Suitable transition metal compounds belonging to Group VB are compoundsthat have the structural formula M″(OR″)_(x)(O)_(y)(X²)_(z) wherein M″is a metal of Group VB of the Periodic Table of Elements, R′ is ahydrocarbyl having from 1 to 18 carbon atoms; X² is halogen; x is 0 oran integer from 1 to 5; y is 0 or 1; and z=(5-x-2y) or 4 or 3 when x=0,y=0. It is especially preferred that M″ be vanadium.

Suitable vanadium compounds encompassed by the above formula include:vanadium oxyhalides, vanadium alkoxides, vanadium carboxylates, vanadiumhalides and mixtures thereof. It is especially preferred that thevanadium-containing compound be vanadium tributyloxy, triisobutylvanadate, vanadium tetrachloride and the like.

This contact between the transition metal-containing compound and themodified organomagnesium-containing support contact product occurs at atemperature from about 15° to about 120° C. More preferably, thetemperature of this contacting step is from about 20° to about 40° C.The time employed for contacting with the transition metal-containingcompound is at least about 5 minutes. Most preferably, the time of thiscontacting step is from about 30 to about 60 minutes.

The concentration range of transition metal-containing compound employedin the present invention is from about 0.1 to about 10 mmole transitionmetal compound per gram support. More preferably, the concentration oftransition metal compound used in this contacting step is from about 0.5to about 1.0 mmole transition metal compound per gram support.

It should be noted that the above order of addition represents oneembodiment for preparing the polymerization catalyst of the presentinvention. It is also within the contemplation of the present inventionto change the order of addition so that the alcohol or silane componentis added after contact with the transition metal-containing component.In that embodiment of the present invention, the reaction sequence wouldbe to first contact the treated support with the above mentionedorganomagnesium compound or complex, contact that product with atransition metal compound and thereafter add the alcohol or silane.

It is also within the contemplation of the present invention to contactthe treated support with the alcohol or silane and then to contact thatcontact product with an organomagnesium compound or complex and atransition metal compound.

The solid ethylene polymerization catalyst is then recovered bydecantation, filtration, evaporation or like recovery techniques, driedat a temperature of from about 15° to about 120° C., and then it is usedin the polymerization of ethylene and the at least one C₄₋₈ comonomer.Specifically, the polymerization occurs by contacting ethylene and theat least one C₄₋₈ comonomer in the presence of the above describedethylene polymerization catalyst, a cocatalyst and, optionally, acocatalyst modifier under ethylene polymerization conditions.

It should be appreciated that all the treatment steps in the formationof the ethylene polymerization catalyst of this invention, the contactof support with the organomagnesium compound or complex, alcohol orsilane and the transition metal compound, involve contact between asolid, a support material, and a liquid. This is because each of thecompounds that are contacted with the support material are liquids, orare soluble in an inert hydrocarbon solvent under the conditionsemployed by the present process. As such, no ball-milling or other solidmixing is required. Ball-milling is an expensive and difficult operationtypically used in the formation of polymerization catalysts of the priorart. Those skilled in the art are aware, in the case where a hydrocarbonis employed, that the solvent may be allowed to remain with the reactionmass or can be removed by decantation, filtration, evaporation, or thelike.

The cocatalysts employed by the present invention in activating theethylene polymerization catalyst are conventional aluminum-containingcompounds well known in the art. The aluminum-containing cocatalysts arepreferably alkylaluminum-containing compounds. Alkylaluminum-containingcompounds suitable for the present process include trialkylaluminum,alkylaluminum halide, alkylaluminum hydride, aluminoxane (either cyclicof linear) or mixtures thereof. More preferably, the cocatalyst is atrialkylaluminum compound. Of the trialkylaluminum compounds,triethylaluminum (TEAL) is particularly preferred.

The molar ratio of aluminum-containing cocatalyst to transition metal inthe solid catalyst is from about 0.01 to about 500. More preferably, themolar ratio of cocatalyst to transition metal in said solid catalyst isfrom about 10 to about 120.

The cocatalyst modifiers that may be optionally employed by the presentinvention are hydrocarbyl alkoxysilanes. It is again emphasized thatwhen an alcohol is employed in preparing the polymerization catalyst thecocatalyst modifier is not optional. Rather it is required in thatembodiment of the present invention. Preferred hydrocarbyl alkoxysilanesinclude: hydrocarbyl trialkoxysilanes, dihydrocarbyl dialkoxysilanes andtrihydrocarbyl alkoxysilanes. Of the hydrocarbyl trialkoxysilanes,diisopropyldimethoxysilane (DIPS) is highly preferred.

When a cocatalyst modifier is employed, the molar ratio of saidcocatalyst modifier to transition metal in said solid catalyst is fromabout 0.01 to about 100. More preferably, the molar ratio of cocatalystmodifier to transition metal in said solid catalyst employed is fromabout 0.1 to about 10.

The polymerization process can be conducted in either the gas phase(stirred or fluidized bed) or solution phase. When gas phasepolymerization is employed, a single or multiple reactor connected inparallel or series may be employed. The conditions of gas phasepolymerization employed in the present invention include any that haveheretofore been utilized. Examples of suitable conditions for operatingin the gas phase that can be employed herein are disclosed, for example,in U.S. Pat. No. 5,258,345 to Kissin, et al., the contents of which arebeing incorporated herein by reference.

When solution polymerization is employed, the polymerization is carriedout in a liquid organic medium in which the solid ethylenepolymerization catalyst is suspended using any slurry polymerizationconditions heretofore utilized. A pressure sufficient to maintain theorganic diluent and at least a portion of the comonomer in the liquidphase is maintained. Examples of typical operating conditions for slurrypolymerization that can be employed herein are described in EPO 848 021A2, the contents of which are being incorporated herein by reference.

The above ethylene polymerization catalyst and polymerization processprovide the ethylene copolymer resin having the above-described uniquemelt elastic properties. Hence, the ethylene copolymer resin has all ofthe properties mentioned hereinabove which include having a density of0.930 cc/g or lower and having a network structure. Moreover, theethylene copolymer resin exhibits the unique melt elastic propertiesmentioned hereinabove. Such melt elastic properties distinguish theinventive copolymer resin from any commercially known copolymer sincethe same do not exhibit the above-mentioned melt elastic properties.

Another aspect of the present invention relates to a high-impactstrength film that can be produced from the ethylene copolymer resin ofthe present invention. Specifically, the high-impact strength film isformed from the pellet of the ethylene copolymer resin of the presentinvention, and it exhibits improvement in film properties and/orprocessability. Specifically, the film of the present invention exhibitsa dart impact strength of greater than about 300 g/mil and a MD tear ofgreater than about 300 g/mil. In one embodiment of the presentinvention, the film has a dart impact strength greater than a bout 350g/mil and a modulus of elasticity of from about 20 to about 35 Ksi.

The film is formed in the present invention using a single layer blownfilm extrusion line which operates under the following conditions:

1 mil, 2.5 Blow-up-ratio, 150 lb/hr, 8 inch die, 100 mil die gap, duallip air ring, 16 inch frostline height, 420° F. melt temperature, 3.5inch extruder with a barrier screw and a Maddock mixing section.

The resin and film properties are determined using standard ASTMprocedures. Specifically, the following ASTM procedures are used in thepresent invention:

Melt Index D-1238 Density D-2389 Film Impact/Free Falling Dart D-1709MD-Tear D-1922 Modulus of Elasticity, 1% D-882 secant

The following examples are given to illustrate the scope of thisinvention. Because these examples are given for illustrative purposesonly, the present invention should not be limited thereto.

EXAMPLE 1

In this example, the ethylene polymerization catalyst of the presentinvention was used in copolymerizing ethylene and 1-hexene or 1-buteneand the results thereof are compared to polymers prepared from catalystsdisclosed in U.S. Pat. Nos. 5,336,652 to Mink, et al. and 4,335,016 toDombro.

I. Laboratory Catalysts Tested in Bench Scale Reactor Inventive Catalystpreparations—Catalysts 1-14.

Davison 948 silica was treated with 20 wt % hexamethyldisilazane(HMDS)and was dried in a quartz glass tube equipped with glass frit. Thesilica was fluidized with a stream of N₂ and placed in a vertical tubefurnace. The silica was heated to 150° C. over 4 hours, held at 156° C.for 4 hours, and cooled to room temperature over 1 hour.

Davison XPO 2406 silica was treated with 12 wt % hexamethyldisilazane(HMDS) and was dried in a quartz glass tube equipped with glass frit.The silica was fluidized with a stream of N₂ and placed in a verticaltube furnace. The silica was heated to 150° C. over 5 hours, held at150° C. for 4 hours, and cooled at room temperature over 2 hours.

The catalysts were prepared in a three-neck round bottom flask with apaddle type stirrer. All glassware was oven dried and assembled hotunder a nitrogen purge. The left and right joints were fitted,respectively, with a nitrogen source and a vent to a mineral oilbubbler. The vent was also used to add the ingredients and to remove thefinished catalyst. The glassware was purged 1 hr prior to starting thecatalyst synthesis. Typically, 4 to 8 grams of HMDS treated silica wasadded to the flask followed by about 8 ml of heptane/gram of silica andthe slurry was stirred at about 160 rpm. The appropriate amount ofdialkyl magnesium in heptane was added by syringe. After 30 minutes, theappropriate amount of silane in heptane was added. After 30 minutes, theappropriate amount of TiCl₄ in heptane was added. After 30 minutes theheptane was distilled off with a sweep of N₂ at 100° C.

Catalysts 1-12 were prepared on Davison 948 silica and dried at 100° C.

Catalysts 1-9, 11 and 12 were prepared with dibutylmagnesium (DBM).

Catalysts 1-6, 10-13, were prepared with Si(QEt)₄(TEOS).

Catalysts 7 and 8 prepared with MeSi(OEt)₃(MTEOS).

Catalyst 9 prepared with (isopropyl)₂Si(OME)₂(DIPS).

Catalysts 10, 13, and 14 were prepared with butylethylmagnesium (BEM).

Catalyst 11 addition order was Si(OEt)₄, dibutylmagnesium, and TiCl₄.

Catalysts 13 and 14 were prepared on Davison XPO silica and dried at 85°C.

Catalyst 14 prepared with Si(OBu)₄(TBOS).

Amounts of mmole/gram silica. Catalyst Amount of Mg Amount of Si Amountof TiCl₄ 1 .65 DBM .16 TEOS .65 2 .65 DBM .16 TEOS .65 3 .90 DBM .23TEOS .90 4 .90 DBM .10 TEOS .90 5 .40 DBM .10 TEOS .40 6 .65 DBM .16TEOS .65 7 .70 DBM .40 MTEOS 1.0 8 1.0 DBM 1.0 MTEOS 1.0 9 .50 DBM .12DIPS .50 10 .50 BEM .12 TEOS .50 11 .50 DBM .12 TEOS .50 12 .50 DBM .12TEOS .50 13 .50 BEM .12 TEOS .50 14 .50 BEM .12 TBOS .50

Bench Scale Polymerization

The reactor used was a 3.3 liter vessel with a helical agitator,thermocouple, and a valve for removing the resultant polymer. The jacketcontained water which was recirculated for temperature control at 82° C.1.5 ml of 25% triethylaluminum in heptane was added by syringe to theseed bed. The catalyst was added to the polymer bed through apolyethylene tube. The agitator was started and 163 psi of N₂ was addedto the reactor. Next, 18.9 psi of hydrogen was added to the reactor; andthereafter 80 ml of hexene was added to the reactor. Ethylene was thenadded to give 300 psi reactor pressure. A mixture of 12 wt % hexene inethylene was fed into the reactor to maintain 300 psi on the reactor.When the total ethylene feed reached about 400 grams, the ethylene feedwas stopped and the reactor was cooled and vented. About 448 grams ofpolymer was drained out of the reactor and the polymerization wasrepeated three more times to remove the original seed bed. The fourthbatch of polymer that was drained from the reactor was submitted fortesting.

For inventive catalysts 1-6, (see Table 1) it can be seen that theinventive catalysts show good activity, good comonomer response, goodbulk density and produce polyethylene narrow molecular weightdistributions.

Bench Scale Slurry Polymerizations With Hexene:

Polymerizations were carried out in a 1 gallon Autoclave Engineering®reactor at 80° C. and 300 psi. After purging the reactor with nitrogen,400 ml of hexene was added and hydrogen was, added as a 250 psi pressuredifferential from a 300 cc vessel. About 0.7 liter of isobutane wasadded and the stirrer was started. Ethylene was added to give a totalreactor pressure of 260 psi. 192 ml of 1.56 M triethylaluminum inheptane was flushed into the reactor with about 200 ml of isobutane.After 1 minute, the catalyst was flushed into the reactor with 200 ml ofisobutane to give a total isobutane volume of 1.1 liters. Ethylene wasallowed to feed into the reactor to maintain 300 psi. The reaction wasterminated by stopping the ethylene feed and venting the reactor.Reactivities were calculated based on grams polymer recovered in onehour/grams of catalyst weight. Melt index (MI, grams/10 minutes) andhigh load melt index (HLMI, grams/10 minutes) measurements were madeusing ASTM method D1238-86.

Comparison of,catalysts 7, 8, 9 and 12 (see Table 1) show that severalother alkoxy silane compounds can be used in the inventive catalysts.TEOS, MTEOS and DIPS show narrow molecular weight distributions.Comparison of catalysts 11 and 12 show that the addition order isunimportant and both catalysts show good reactivity and narrow molecularweight distributions. Comparison of catalysts 10 and 12 show that theexact dialkylmagnesium compound is unimportant and both catalysts usingdifferent magnesium compounds show good reactivity and narrow molecularweight distributions.

Bench-scale Slurry Polymerizations With Butene:

Polymerizations were carried out in a 1 gallon Autoclave Engineering®reactor at 75° C. and 335 psi. After purging the reactor with nitrogen,200 ml of butene was added and hydrogen was added as a 200 psi pressuredifferential from a 300 cc vessel. About 1.0 liter of isobutane wasadded and the stirrer was started. Ethylene was added to give a totalreactor pressure of 300 psi. 1.92 ml of 1.56 M triethylaluminum inheptane was flushed into the reactor with about 150 ml of isobutane.After 1 minute, the catalyst was flushed into the reactor with 150 ml ofisobutane to give a total isobutane volume of 1.3 liters. Ethylene wasallowed to feed into the reactor to maintain 335 psi. The reaction wasterminated by stopping the ethylene feed and venting the reactor.Reactivities were calculated based on grams polymer recovered in onehour/grams of catalyst weight. Melt index (MI, grams/10 minutes) andhigh load melt index (HLMI, grams/10 minutes) measurements were madeusing ASTM method D1238-86.

Comparison of catalysts 13 and 14 show that TBOS works equally well asTEOS. In addition, catalysts 13 and 14 also show that,the amount of HMDSused to treat the silica can be reduced from 20 to 12 wt % and the typeof silica can be varied from 948 to XPO.

Dombro Catalyst Synthesis (CE1):

704° C. dried 948 silica/0.65 mM BEM/0.16 mM Si(OEt)₄/0.65 mM TiCl₄

About 20 grams of Davison 948 silica was placed in a 1 inch diameterquartz glass tube equipped with a glass frit. The silica was fluidizedwith a stream of N and placed in a vertical tube furnace. The silica washeated to 704° C. over 6 hours, held at 704° C. for 6 hours, and cooledto room temperature over 6 hours.

The catalyst was prepared in a three-neck round bottom flask with apaddle-type stirrer. All glassware was oven dried and assembled hotunder a nitrogen purge. The left and right joints were fitted,respectively, with a nitrogen source and a vent to a mineral oilbubbler. The vent was also used to add the ingredients and to remove thefinished catalyst. The glassware was purged for about 1 hr. prior tostarting the catalyst synthesis. 4.805 grams of the 948 silica was addedto the flask followed by about 40 ml. of heptane and the slurry wasstirred at about 160 rpm. 4.73 ml of a 0.66 M butylethylmagnesium (BEMg)in heptane was added by syringe. After 30 minutes, 0.77 ml of a 1.0 Msolution of Si(OEt)₄ in heptane was added. After 30 minutes, 3.12 ml ofa 1.0 M solution of TiCl₄ in heptane was added. After 30 minutes, theheptane was distilled off with a sweep of N₂ at 100° C.

Mink Catalyst Synthesis (CE2):

948 silica/3.67 mM TEA/0.7 mM BEM/0.17 mM Si(OEt)₄/0.7 mM TiCl₄

The method used for treating silica with triethylaluminum is describedby A. Noshay and F. J. Karol in “Transition Metal CatalyzedPolymerizations Ziegler-Natta and Metathesis Polymerizations.” CambridgeUniversity Press, New York, N.Y., edited by R. P. Quirk, 1988, pp.396-416.

The catalyst was prepared in a three-neck round bottom flask with apaddle-type stirrer. All glassware was oven dried and assembled hotunder a nitrogen purge. The left and right joints were fitted,respectively, with a nitrogen source and a vent to a mineral oilbubbler. The vent was also used to add the ingredients and to remove thefinished catalyst. The glassware was purged for about 1 hr. prior tostarting the catalyst synthesis. 10.236 grams of Davison 948 silica wasadded. The flask was purged for 30 minutes and about 80 ml of heptanewas added. The slurry was stirred at about 160 rpm. 24.1 ml of a 1.56 Mtriethylaluminum solution in heptane was added. After 30 minutes, theslurry was warmed to 40° C. 10.86 ml of a 0.66 M butylethylmagnesium inheptane was added. After 30 minutes, 1.74 ml of a 1.0 M solution ofSi(OEt)₄ in heptane was added. After 30 minutes, 7.16 ml of a 1.0 Msolution of TiCl₄ in heptane was added. After 30 minutes the temperaturewas increased to 55° C. and the heptane was distilled off with a sweepof N₂.

CE1 (Dombro) and CE2 (Mink) showed lower H₂ response, lower reactivityand lower polymer bulk density than the inventive catalysts j and 2. CE1showed lower comonomer response, CE2 produced a density similar tocatalysts 1 and 2 but produced a polymer with a broader molecular weightdistribution than catalysts 1 and 2.

II. Scale-up Catalysts—Inventive Catalyst 15:

HMDS 948/0.65 mM BEM/0.16 mM Si(OEt)₄/0.65 mM TiCl₄

A steel reactor was purged for 6 hrs with N₂. HMDS Davison 948 silicathat was dried at 150° C. was added and the stirrer was started at 100rpm. 5 lbs. of heptane/lb. of silica was added and the slurry wasstirred for 30 minutes. The appropriate amount of butylethylmagnesium(10% in heptane) was added and the slurry was stirred for 30 minute. Theappropriate amount of Si(OEt)₄(5% in heptane) was added and the slurrywas stirred for 30 minutes. The appropriate amount of TiCl₄ (10% inheptane) was added and the slurry was stirred for 30 minutes. Thecatalyst was dried at 99° C. with a sweep of N₂.

Dombro Catalyst Synthesis (CE3):

700 dried 948/0.65 mM BEM/0.16 mM Si(OEt)₄/0.65 mM TiCl₄

A 5 gallon steel reactor was purged for 6 hrs with N₂. 2 lbs. of 700° C.dried Davison 948 silica was added and the stirrer was started at 100rpm. 10 lbs. of heptane was added and the slurry was stirred for 30minutes. 1.43 lbs. of butylethylmagnesium (10% in heptane) was added andthe slurry was stirred for 30 minutes. 1.33 lbs. of Si(OEt)₄ (5% inheptane) was added and the slurry was stirred for 30 minutes. 2.47 lbs.of TiCl₄ (10% in heptane) was added and the slurry was stirred for 30minutes. The catalyst was dried at 99° C. with a sweep of N₂. A secondpreparation of this catalyst was made following the same procedurecalled CE3-2.

Mink Catalyst Synthesis (CE4):

948 silica/3.67 mM TEA/0.7 mM BEM/0.17 mM Si(OEt)₄/0.7 mM TiC₄

Glassware was oven dried and purged with N₂ for 1 hour. 250 g undried948 silica was charged to a 3 liter round bottom reaction flask. Theflask was purged with N₂ for 1 hour with stirring at about 100 rpm and500 ml hexane was added. 582 ml of 25% triethylaluminum in heptane wasadded. After 30 minutes, the slurry was heated to 40° C. 275 ml ofbutylethylmagnesium (10% in heptane) was added. After 30 minutes, 9.5 mlof Si(OEt)₄ was added. After 30 minutes, 19.5 ml of TiCl₄ was added.After 30 minutes, the slurry was heated to 55° C. and the catalyst wasdried with a stream of N₂. A total of three batches of this catalyst wasprepared and blended together for testing.

Gas-phase Fluidized Bed Polymerizations:

Gas-Phase polymerizations were carried out as described, in U.S. Pat.Nos. 4,001,382, and 4,302,566.

The reaction temperature used was 180° F. with a fluidized velocity of1.7 ft/sec. The ethylene, hydrogen and hexene concentrations wereadjusted to produce a target polymer with a 0.915 g/cc density and a 1.0melt index.

TABLE 2 Pro- den- Mole % Mole % Mole % Catalyst ductivity MI sity ERethylene hydrogen hexene 15 6100 1.16 .915  .71 28.3 5.8 5.8 CE3 19001.35 .925 1.24 28.0 5.4 6.8 CE3-2 1100 1.11 .926 — 27.0 5.8 7.0 CE4  300.80 .926 1.29 28.0 5.4 6.8

Inventive catalyst 15 showed good catalyst activity and good comonomerresponse as well as narrow molecular weight distribution. CE3 (Dombro)and CE4. (Mink) catalysts had poor catalyst productivity and such poordensity response that the target products could not be produced. A newbatch of CE3 (Dombro) catalyst was made to verify the results from thefirst batch. Once again hexene response and catalyst productivity werevery poor.

EXAMPLE 2

In this example, the melt elastic properties of the ethylene copolymerresin of the present invention were compared with prior art ethylenecopolymers. Both the powder and pelletized forms were investigated.Other pertinent physical data are also reported herein and compared tocommercial ethylene copolymer resins.

In this example, all the resins were prepared using a gas-phasefluidized bed polymerization process like the one described inExample 1. Resins. 1-4 and 10-11 represent prior art or commercialresins; whereas resins 5-9 represent resins of the present invention.

Resins 1 and 4 were prepared from a standard polymerization catalystusing a gas phase process. resins 2 and 3 were prepared using aconventional catalyst such as described in U.S. Pat. No. 4,374,753 toPullukat, et al. and resins 10-11 are commercially available highperformance hexene LLDPE resins.

Resins 5-6, which represent the present invention, were prepared from acatalyst system which contained silica/MAGALA/butanol/TiCl₄ as the solidcatalyst component and DIPS as a cocatalyst modifier.

Resins 7-9, which also represent the present invention, were preparedusing a catalyst similar to catalyst 10 of Example 1.

The properties of each resin determined using the techniques definedhereinabove are reported in Table 3 and are graphically illustrated inFIGS. 1-6.

As shown in FIGS. 1-4, the resins of the present invention typicallyhave higher impact, more rubber phase and smaller interparticle rubberdistance than prior art resins.

Of significance is that the ethylene copolymer resins of the presentinvention, resins 5-9, exhibited the unique melt elastic propertiesmentioned above, whereas prior art resins 1-4 and 10-11 did not exhibitthe unique melt elastic properties. Specifically, as shown in FIG. 5,the powder form of resins 5-9 all have ER values of 0.9 or below whichundergo an increase in ER when pelletizing the powder.

Unlike the resins of the present invention, prior art resins 1-4 and10-11 do not exhibit the same. Instead, when an increase in ER valuefrom powder to pellet is observed, prior art powders had an initial ERvalue of greater than 0.8 (i.e. ER>0.8, if % ER shift was greater than0), or when the prior art powder ER is 0.8 or below, the prior artresins did not exhibit an increase in ER in going from the powder to thepellet, (i.e. % ER shift=0, if ER is 0.8 or less).

In addition to the above melt elastic properties, the inventive resinsexhibited the melt elastic properties shown in FIG. 6. Specifically, thepelletized forms of resins 5-9 exhibited a 10-30% reduction in ER tovalues below 1.0 after rheometric low shear modification.

In contrast thereto, prior art pelletized samples had ER>1.0, if % ERshift reduction was less than 0, or they had % ER shift reduction=0, ifER was is less than 1.0.

Another important property of the resins of the present invention isthat an increase in ER is observed in going from the powder to thepellet. This increase is almost completely reversible when the pellet isdissolved in xylene (See, Table 4). In the case of prior art resins, theER values remained unchanged when going from pellet to solutiondissolved pellet.

TABLE 4 Effect of Xylene Dissolution on ER Resin 1 Resin 11 Resin 9Powder ER 0.82 N/A 0.76 Pellet ER 0.82 0.59 1.14 ER of Xylene 0.85 0.590.84 Dissolved Pellet

The above embodiments and examples are given to illustrate the scope andspirit of the present invention. These embodiments and examples willmake apparent, to those skilled in the art, other embodiments andexamples. These other embodiments and examples are within the scope ofthe present invention therefore, the instant application should belimited only by the appended claims.

TABLE 1 Bulk Catalyst MI MIR density Reactivity ER density 1 .80 29.6.9219 2234 .86 .422 2 .75 29.6 .9202 1937 1.0 .422 3 .65 31.8 .9206 2979.90 .423 4 .89 32.6 .9218 2606 1.0 .376 5 .56 33.4 .9168 1493 1.0 .386 6.75 33.6 .9164 2139 .98 .396 7 .70 27.0 —  682 — — 8 .40 27.5 .9366  295— — 9 .70 24.0 .9365 1762 .73 — 10 1.19 27.2 — 1144 — — 11 1.78 27.3 —2480 .77 — 12 1.19 25.2 — 1058 .83 — 13 .57 25.3 .9221 1751 .72 — 14 .5525.2 .9274 1777 — — CE1 .38 29.7 .9251  558 1.0 .332 CE2 .34 28.2 .9220 266 .92 .325

TABLE 3 LIST OF RESIN AND FILM DATA % ER- ER- MD- Melt Film Rubber ER,ER, Shift, ER-After Shear Shear Tear, Modulus, Resin Index DensityImpact (SEM) Powder pellet % modification Mod., % g/mil Ksi 1 1.0 0.918188 ± 15 2.7 ± 0.7 0.82 0.82 N/A 0.82 0.0 335 ± 40 29.0 ± 1.0 2 0.70.9163 266 ± 28 9.3 ± 5.1 1.0  1.3 30 1.18  −9 245 ± 7  31.0 ± 1.0 3 0.70.9146 356 ± 13 12.5 ± 2.0  1.06 1.54 45 1.12 −27 265 ± 7  30.0 ± .07 40.9 0.915 336 ± 6  5.0 ± 1.5 0.86 1.26 47 1.10 −13 320 ± 14 28.0 ± 0.9 51.0 0.917 355 ± 56 18.7 ± 1.0  0.68 1.2 76 0.25 −21 339 ± 8  28.0 ± 1.06 0.75 0.9155 590 ± 85 23.1 ± 3.6  0.67 1.1 64 0.76 −31 366 ± 17 27.6 ±1.1 7 1.0 0.919 196 ± 9  5.1 ± 0.5 0.76 0.84 11 0.76 −10 340 32.2 ± 1.08 1.0 0.917 331 ± 8  8.9 ± 1.8 0.76 0.98 29 0.80 −18 355 ± 7  28.8 ± 0.79 1.0 0.915 602 ± 40 19.8 ± 2.0  0.76 1.14 50 0.82 −28 380 ± 14 25.6 ±0.2 10 0.95 0.917 476 ± 35 3.0 ± 1.0 N/A 0.68 N/A 0.68 0.0 420 ± 34 26.8± 1.1 11 1.1 0.917 462 ± 88 N/A N/A 0.61 N/A 0.61 0.0 429 ± 31 25.7 ±1.1 1. All films made under same conditions: 1 mil, 2.5 Blow-Up-Ratio,150 lb/hr, 8″ die, 100 mil die gap, dual lip air ring, 16″ frostlineheight, 420° F. melt temperature, 3.5″ extruder with a barrier screw anda Maddock mixing section. 2. All resin and film testing performed perstandard ASTM procedures: D-1238 (Melt Index), D-2839 (Density), D-1709(Film Impact/Free Falling Dart Drop), D-1922 (Tear) and D-882 (Modulusof Elasticity, 1% secant). 3. % Rubber determined by Scanning ElectronMicroscopy (SEM) on etched sections microtomed from melt-pressedpellets. 4. Rheometric shear modification performed as described hereinfor 60 minutes.

What is claimed is:
 1. An in-situ prepared ethylene copolymer resincomprising ethylene, as the major component, and at least one C₄₋₈comonomer with the proviso that said resin, when in pelletized form, hasa reduction in melt elasticity (ER) of 10% or more upon a rheometric lowshear modification or solution dissolution and has a final ER value of1.0 or less after the rheometric low shear modification or solutiondissolution.
 2. An in-situ prepared ethylene copolymer resin comprisingethylene, as the major component, and at least one C₄₋₈ comonomer withthe proviso that said resin, when in reactor-made form, exhibits atleast a partially reversible Increase of 10% or more in melt elasticity(ER) when pelletizing the same compared with before pelletizing, andsaid resin, when in pelletized form, has a reduction in ER of 10% ormore upon a rheometric low shear modification or solution dissolutionand has a final ER value of 1.0 or less after the rheometric low shearmodification or solution dissolution.
 3. The in-situ prepared ethylenecopolymer resin of claim 2 wherein said reactor-made material is eithera powder, a slurry or a solution of said resin.
 4. The in-situ preparedethylene copolymer resin of claim 1 wherein said comonomer is 1-hexene.5. The in-situ prepared ethylene copolymer resin of claim 1 wherein saidethylene copolymer resin has a base polymer density of about 0.930 g/cm³or below.
 6. The in-situ prepared ethylene copolymer resin of claim 5wherein said ethylene copolymer resin has a base polymer density of fromabout 0.920 g/cm³ or below.
 7. The in-situ prepared ethylene copolymerresin of claim 6 wherein said ethylene copolymer resin has a basepolymer density of from about 0.917 g/cm³ or below.
 8. The in-situprepared ethylene copolymer resin of claim 1 wherein said ethylenecopolymer includes a network structure.
 9. The in-situ prepared ethylenecopolymer resin of claim 8 wherein said network structure is formed dueto a rubber phase present in said ethylene copolymer resin.
 10. Thein-situ prepared ethylene copolymer resin of claim 1 wherein saidethylene copolymer comprises 15 vol. % or greater of a rubber phase. 11.The in-situ prepared ethylene copolymer resin of claim 10 wherein saidrubber phase contains from about 35 alkyl branches per 1000 total carbonatoms.
 12. The in-situ prepared ethylene copolymer resin of claim 1wherein said low shear modification is carried out in a rheometercapable of operating at rates of less than 1.0 sec⁻¹ for a time periodof about 10 to about 60 minutes.
 13. The in-situ prepared ethylenecopolymer resin of claim 10 wherein said ethylene copolymer resin has abase polymer density of from about 0.920 g/cm³ or below.
 14. The in-situprepared ethylene copolymer resin of claim 10 wherein said rubber phaseincludes rubber particles having an average radius of about 0.05 toabout 0.25 micrometers.
 15. A film prepared from the ethylene copolymerresin of claim 1, wherein said film is characterized as having an impactstrength of at least about 300 g/mil or greater and a MD tear of atleast about 300 g/mil or greater.
 16. The film of claim 15 wherein saidcomonomer is 1-hexene.
 17. The ethylene copolymer resin of claim 1wherein said resin is prepared by conducting ethylene and at least onC₄₋₈ comonomer in the presence of an ethylene polymerization catalyst, acocatalyst, and optionally a cocatalyst modifier under ethylenepolymerization conditions, wherein said ethylene polymerization catalystis obtained by: (a) contacting a support material with an organosiliconcompound to effectuate reduction of surface hydroxyl groups present onsaid support material; (b) contacting the product of (a) with adialkylmagnesium compound or complex; (c) contacting the product of (b)with an alcohol or a hydrocarbyloxyhydrocarbylsilane; and (d) contactingthe product of (c) with a transition metal compound, with proviso thatwhen an alcohol is employed said cocatalyst modifier is required. 18.The ethylene copolymer resin of claim 17 wherein steps (c) and (d) arereversed as follows: (c) contacting the product of (b) with a transitionmetal compound; and (d) contacting the product of (c) with an alcohol orhydrocarbyloxyhydrocarbylsilane.
 19. The ethylene copolymer resin ofclaim 17 wherein steps (b) and (c) are reversed as follows: (b)contacting the product of (a) with an alcohol orhydrocarbyloxyhydrocarbylsilane; and (c) contacting the product of (b)with a dialkylmagnesium compound or complex.
 20. The ethylene copolymerresin of claim 17 wherein said cocatalyst is an aluminum-containingcompound.
 21. The ethylene copolymer of claim 20 wherein saidaluminum-containing compound is triethylaluminum.
 22. The ethylenecopolymer of claim 17 wherein said optional cocatalyst modifier is ahydrocarbyloxyhydrocarbylsilane.
 23. The ethylene copolymer of claim 22wherein said hydrocarbyloxyhydrocarbylsilane isdiisopropyldimethyoxysilane (DIPS).
 24. The ethylene copolymer of claim17 wherein said contact is carried out in a gas phase or in solution.25. An ethylene copolymer resin that (a) comprises ethylene, as themajor component, and at least one C₄₋₈ α-olefin comonomer; (b) containsa network structure having greater than about 15 vol. % of a rubberphase; (c) when in a pelletized form, has greater than about 10% or morereduction in melt elasticity (ER) upon a rheometric low shearmodification or solution dissolution has a final ER less than about 1.0after the rheometric low shear modification or solution dissolution; (d)when in a reactor made form, exhibits at least partially reversibleincrease of greater than about 10% of ER before pelletizing comparedwith after pelletizing; and (e) has a density less than about 0.930g/cm³.